Automatic gain control circuits are utilized to solve a number of problems in single bipolar transistor crystal oscillators. For example, the amplitude of the oscillator output will be controlled, eliminating problems with variations in mixer injection level produced by crystal resistance and transistor current gain tolerances. Further, crystal dissipation can be held at a low level without sacrificing other parameters such as warp range or output level stability. Controlling the crystal dissipation is important because high levels of crystal dissipation degrade frequency stability and further cause aging and spurious responses.
Prior art automatic gain control circuits make use of the bipolar transistor current gain going to zero as collector current goes to zero. All known prior art circuits use at least one active device for amplification and another to control the collector current of the oscillator transistor. This use of several active devices in the prior art circuits increases both the size and cost thereof.